The properties of central inspiratory inhibition during the expiratory phase will be studied in more detail, using reflex testing with a wider range of values of preceding tidal volume and inspiratory time, and under both normocapnic and hypercapnic conditions. Using more discriminating microelectrodes, we will study the neurons of the medial solitary tract nucleus, characterizing their functional properties and how these may differ between those that project to NPB and those that do not. To test the hypothesis that the very late inspiratory neuron is the inspiratory "off-switch" unit, we will determine how the activity of such cells is affected by stimuli which alter inspiratory duration (lung inflation, deflation, pontine electrical stimulation). Using two microelectrodes, we plan to study the electrophysiology of the sheet organization of FTL. Crosscorrelation of the activities of cells within one sheet and within adjacent sheets will be performed to detect possible interactions.